Schedule Feb 17, 2012
A New Model of Local Group Dwarfs. I. Gas depletion
Matthew Nichols (Univ. of Sydney), J. Bland-Hawthorn (Univ. of Sydney)

A recent survey of the Galaxy and M31 reveals that more than 90% of dwarf galaxies within 270 kpc of the host galaxy are deficient in HI gas. At such an extreme radius, the density of coronal halo gas is an order of magnitude too low to remove HI gas through ram pressure stripping for any reasonably orbit distribution. However, all dwarfs are known to have an ancient stellar population (> 10 Gyr) from early epochs of vigorous star formation which, through heating of HI, could allow a tenuous hot halo to strip this gas. Such gas, preferentially stripped towards perigalacticon, may be able to be reaccreted later fueling future bursts of star formation. Our model looks at the evolution of these dwarf galaxies analytically as the host-galaxy dark matter halo and coronal halo gas builds up over cosmic time. Such a model is able to explain the observed radial distribution of gas-deficient and gas-rich dwarfs around the Galaxy and M31 if the dwarfs fell in at high redshift.

Nichols, M., & Bland-Hawthorn, J. 2011, ApJ, 732, 17


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